In some industrial and laboratory environments workers are exposed to corrosive or contaminating liquids or sometimes solid particles as may occur in welding, abrading, grinding and the like. For industrial safety, workers are usually required to wear goggles and/or use shields between their upper body and head and the liquid or solid source of potential worker injury.
A special example of a protective shield is the hood used in electric arc welding situations. Hoods include a head band which ordinarily fits around the head of the welder who may or may not have a cloth cap to cover his head. The hood itself is attached to the head band and is similar in shape to half of a hollowed out watermelon. A slit at eye level through the hood provides an opening for the welder to view the electric arc. The eye level slit is covered by a rectangle of blackened glass, polycarbonate, cellulose polyonate, acetate or the like. The glass rectangle is darkened to shield the welder's eyes from the bright light of the arc. The object of the large hood is to protect the face and neck of the welder from sparks. If a hat is worn it is usually wool because wool will not burn whereas cotton will smolder and burn.
Usually gas welding will only use a set of goggles to protect the eyes of the welder because there is not such a proliferation of sparks as occurs with electric welding.
When using corrosive chemical materials (usually liquid), workers are often required to wear face shields which extend from forehead to below the chin and those shields are often composed of clear polycarbonate or the like. The means for attaching the face shield to the head of the worker is essentially the same as is used with hoods of welders used in electric arc welding, namely, adjustable head bands.
In some industrially used apparatus a face shield which is vertically tiltable is rigidly mounted on a "hard hat". A hard hat is a plastic or metal head covering worn by workers in areas where there is a potential for objects being dropped from above. The hard hat is intended to prevent the worker from being badly injured because of something dropping onto his head from above. Attaching a heavy polycarbonate face shield to a hard hat which a worker must wear all during his shift of work is merely one more physically tiring burden to be borne by the worker. Worker fatigue is to be avoided because it is a contributing factor in many industrial accidents.
In addition to the weight of the face shield in combination with the hard hat, the connection which allows the face shield to be tilted upward out of the line of sight of the worker also creates an inherent problem from a safety standpoint. The shield is allowed to tilt because it is not connected along the bill of the hard hat. Should acid splash on the worker, the shield will prevent its direct impact on his face or eye. However, if the acid lands on the front or top of the hard hat it will run down the slope until it drips off the bill of the hard hat and possibly onto the nose or other part of the worker's face. Conventional shields prevent straight line impact; they are not designed to shield against drops running down the hard hat.